Basics of Paralleling

© 2017 Cummins All Rights Reserved

Revised: February 1, 2017

Course Objectives

Participants will be able to:

– Discuss basic paralleling control functions to gain a better understanding of

how paralleling is accomplished

– Explain the advantages of paralleling to enhance the overall system

reliability, performance and flexibility

– Describe how generator set control functions are provided in a distributed

logic architecture to improve paralleling reliability

– Recognize the common building blocks of a backup power system and

their functionalities

CnHm

T, w

EL

Generator Set

Skid

Engine

Alternator

Cooling

Control

Power System

Backup Power

Switchgear Transfer Switches

Utility

Loads

Paralleling

Synchronous operation of two or more generator sets connected together

on a paralleling bus in order to provide power to common loads

Paralleling Switchgear Loads

Paralleling Operation

Generators can be connected to a power plant or another generator source

only when the following conditions are met:

– Waveform

– Phase Sequence

– Speed difference (frequency)

– Phase angle difference

– Voltage amplitude difference

900 180 270 360

Øv

Deg

Source-1

Source-2

t10 t2 t3 t4

v

t

∆V

f1

t10 t2 t3 t4

v

t

f2

A

B CACB

120°120°

A

C BABC

120°120°

Sine

Square

Sawtooth

Synchronization

Synchronization is the mechanism of matching frequency, phase and voltage

of AC power sources

Maintains generator output voltageAutomatic Voltage

Regulator

Maintains engine output speedElectronic

Governor

Electronic Governor (GOV)

Fuel Tank

Pump

T, w

InjectorsSpeed Sensor

Fuel

Electronic

Governor

Automatic Voltage Regulator (AVR)

The output voltage can be

increased or decreased by altering

the strength of the magnetic field

𝜵 × 𝑬 = −𝛿𝑩

𝛿𝑡(𝐹𝑎𝑟𝑎𝑑𝑎𝑦′𝑠 𝐿𝑎𝑤)

Main RotorMain Rotor

AVR

v

t0

DC Current

Output

Magnetic

Flux FieldMain Stator

Exciter Rotor

& Stator

Rectifier

Match Frequency, Phase and Voltage

Synchronizer

CBCBClose signal

Offset

-+Load Side Line Side

Offset

Closed feedback loop:

Hz, Ø & V

Generator Set Control

Synchronizer

Sense line & load

waves:

Frequency Hz

Phase ØVoltage V

AC Network:

480 VAC, 60 Hz, 3Ø

Voltage

Regulator

Electronic

Governor

Hz, Ø

V

Synchronized

Line Side Wave

Load Side Wave

f2

f1

Synchronizing: Phase and Frequency

Adjusting the governor fuel set point

900 270

Ø

v

v

Deg180 360

t10 t2 t3

t4 t

Source-1

Source-2

Speed

Sensor

Prime

Mover

Shaft

-+

Setpoint

1800 RPM ω(t)

Fuel

Actuator

Electronic

Governor

Fuel

+

Offset (t)

Synchronizing: Voltage Amplitude

Adjusting the field excitation

v

t0

Source-1

Source-2

Voltage

Sensor

+-+

Electric

Generator

Setpoint

4.16kV

Excitation

System

Voltage

Regulator

OutputV(t)

Offset (t)

Rotor Position and Output Voltage

ElectricalDegrees = P/2 * MechanicalDegrees P: Number of poles

Main Stator Coils in SlotsAir Gap

SHAFT

S

S

NN900 180 270 360 90 180 270 360

Alternator Shaft Position

(Degrees)

One Wave Cycle

Deg

v

Controlling Speed, Phase and Voltage

Voltage

Sensor

+-+

Speed

Sensor

Prime

MoverElectric

Generator

Generator Set

Shaft

-+

Output

Setpoint

1800 RPMSetpoint

4.16kVω(t)

Excitation

System

Voltage

Regulator

Fuel

Actuator

Electronic

Governor

Fuel

Offset Offset

+

Standby System Simulation: Isolated Bus

Paralleling Sequence of Operation: Isolated Bus

Remote Start

Sync Check

Conditions Met

Engine Cranks & Builds Up

To Rated Speed & Voltage

Gen

Bus Status

Ready to Load

De-energizedFirst Start

Arbitration

EnergizedSynchronize

Close Generator Breaker

& Load Share

First Start

Permission Won

The proportional division of the kW and kVAR total load between multiple

generator sets in a paralleled system

– Load sharing is essential to avoid overloading and stability problems on the generator sets

Load share can be Isochronous or Droop

Load Sharing

2MW Load

2 MW

1 MW

1 MW

0.5 MW

1 MW

0.5 MW

The kW load sharing is achieved by increasing or decreasing fuel to the

engines

The kVAR load sharing is achieved by increasing or decreasing the field

excitation to the alternators

50% kVAR 50% kVAR 50% kVAR

kVAR

Load Share Lines

AVR AVR AVR

50% kW 50% kW50% kW

kW

Load Share Lines

GOV GOV GOV

Load Sharing

Communication

Wires

Energy Management

Po

wer

Req

uir

em

en

ts

Time

Peak Shave

Utility Supplied Power

User Supplied Power

Peak Shave

Base Load

Po

wer

Req

uir

em

en

ts

Time

Base Load

Utility Supplied Power

User Supplied Power

Connecting to the Grid

Base load, peak shave, extended paralleling

Cannot change the grid voltage and frequency

Drive generator sets to match the grid

Infinite

Source:

Frequency

Phase

Voltage

Grid

Match

Grid

Synchronizer

kW Load

Govern Lines

GOV GOV

kVAR Load

Govern Lines

AVR AVR

Peak Shave Mode - Extended Paralleling

Grid Connecting Example

Controller

Utility Import Setpoint:

e.g. 0.5 MW

Read Power

2.5 MW Load

0.5 MW

Grid

kW Load

Govern Lines

GOV GOV

kVAR Load

Govern Lines

AVR AVR

2 MW

1 MW

2 MW

1 MW

Typical Generator Protection Elements

15 – Synchronizer

24 – Volts/Hertz

25 – Synch Check

27 – Undervoltage

32 – Directional Power

40 – Loss of Excitation/Reverse kVAR

46 – Phase Balance Current

47 – Phase Sequence Voltage

50 – Instantaneous overcurrent

51 – Time Overcurrent

59 – Overvoltage

81U/O – Under/Over Frequency

Reverse kWReverse kVAR

Paralleling Control

Paralleling

Genset Protection

Voltage Regulation

Load Sharing

Generator Metering

Generator Set Controller

Engine Protection

Governing

Engine metering

Engine Control Module

Data Link

Human Machine Interface

Data Link

User Interface

Configurations/Settings

Alarms

Start/Stop

Manual Paralleling

Generator Set Paralleling Controls Capabilities

Without a Digital Master Control, generator set control can:

– Parallel with each other

– Synchronize with the grid (single genset) - Base Load/Peak Shave

– Single Load Add/Shed Scheme

– Perform Load Demand

LoadLoad

Grid

Master Control

Is required when:

– Synchronizing multiple generator sets with the utility or multiple utility feeds

– Load and capacity management

– System monitoring and control

– Complex sequence of operation

Load 1

Synchronize

Grid

Master Control

Load 3 Load 4Load 2

Digital Master Control

Digital Master Control

Summary

Governor and AVR are the basic functions on every genset and the

synchronizer, load share and load govern simply adjust the reference

point to them

Paralleling enhances the overall system reliability, performance and

flexibility

Distributed logic architecture in a paralleling system improves the overall

reliability by eliminating single points of failure

Thank You!

Please share your feedback by completing the Power Seminar evaluation form.

© 2017 Cummins All Rights Reserved

Load Demand

Match generating capacity to the load to optimize fuel efficiency and prolong

generator set life

CB

1 MW

CB

1 MW

CB

1 MW

CB

1 MW

CB

1 MW

Load:

1 MW

CB

1 MW

CB

1 MW

CB

1 MW

CB

Capacity: 5MW

0.5 MW1.5 MW3.0 MW3.5 MW4.75 MW

Reference Material:Load Demand

The load demand feature is used to match generating capacity to the

load to optimize fuel efficiency and prolong generator set life while

maintaining correct reserve capacity for the customer’s application

Shutdown sequence can either be a fixed sequence or can be based on

running hours

– Fixed sequence: the sequence can be changed while the system is in operation

– Running hours: attempts to equalize generator set hours over time by exchanging

stopped and running generator sets

To protect system integrity, load demand will restart all generator sets

whenever an overload condition is detected

The minimum amount of capacity to maintain online is adjustable